Ch 7. Alternating Current

Question 1

The root mean square (r.m.s) value of alternating current of equation I = 60sin 100 π t is

Answer 1

60/√2

Question 2

For resonance condition in any L-C-R circuit, the phase difference between applied voltage and current is

Answer 2

Zero

Question 3

The phase difference between current and voltage is only capacitive alternating current circuit is

Answer 3

90•

90 degree

Question 4

The impedance of L-R circuit is

Answer 4

The impedance of the LR series circuit is Z=√R²+(ωL)²

Question 5

In step up transformer, the value of current in secondary coil compared to primary coil is

Answer 5

Less

Question 6

Capacitive reactance is

Answer 6

1/ωC

Question 7

The relation between r.m.s value of alternating current (I r.m.s) and peak value of alternating current ( I₀ ) is

Neeche r.m.s

Answer 7

I r.m.s. = 0.707I₀

Neeche r.m.s

Question 8

Inductive reactance offered by an inductor of inductance L in A.C. circuit of angular frequency ω is

Answer 8

ω.L

Question 9

In an alternating current circuit, the phase difference between current I and voltage is φ then Wattless component of current will be

Answer 9

I sin φ

Question 10

The ratio of root mean square (r.m.s) value and peak value of an alternating current is

Answer 10

1/√2

Question 11

In A.C. circuit, the current and voltage are given by i = 5 cos ωt and V = 200 sin ωt respectively. Power loss in the circuit is

Answer 11

Zero

Question 12

The relation between peak current I₀ and root mean square current I rms is

Neeche rms

Answer 12

I₀ = √2 I rms

Neeche rms

Question 13

The unit of reactance is

Answer 13

Ohm

Question 14

Hot wire ammeter measures

Answer 14

r.m.s. value of A.C.

Question 15

If the equation of an electric current is
I = 0.6 sin 100 πt, the frequency of electric current is

Answer 15

50

Question 16

The ratio of peak value and r.m.s value of ac is

Answer 16

√2

Question 17

The peak voltage of an A.C. is 440 volt. its virtual voltage is

Answer 17

220√2 V

Question 18

In the following Question Nos. 1st to 4th, there are two columns, Column 1st contains 4 questions. You have to match the correct options of these questions as A,B,C and D from column 2nd.

Answer 18

1. Frequency of D.C. = Zero
2. Choke coil = reduces A.C. current
3. Energy density of electric field = 1/2 ε₀ E²
4. 1kWh = 3.6 × 10⁶J

Question 19

Which of the following relations is correct for power factor?

Answer 19

Power factor = True average power/Apparent average power

Question 20

The power factor of L- R circuit is

Answer 20

R/√R² + ω² L²

Question 21

Impedance of L-R circuit is

Answer 21

√R² + ω² L²

Question 22

If φ is the phase difference between A.C. current and e.m.f., then the value of power factor is

Answer 22

Cos φ

Question 23

Dimensional formula of R.C. is

Answer 23

M⁰L⁰T

Question 24

The expression for real average power in an alternating current circuit is

Answer 24

P av = E rms I rms cos φ

Neeche av, rms and rms

Question 25

Power factor is equal to

Answer 25

R/Z

Question 26

Phase difference in (L-R) circuit is

Answer 26

tan⁻¹ (ωL/R)

Question 27

Inductive reactance is

Answer 27

X l = 2πfL

Neeche l

Question 28

Inductive reactance for direct current is

Answer 28

Zero

Question 29

Which of the following is correct for transformer?

Answer 29

It increases or decreases A.C. voltage

Question 30

Which quantity decreases in step-down transformer?

Answer 30

Voltage

Question 31

If N₁ and N₂ are number of primary and secondary coils of a step-up transformer, then

Answer 31

N₂ > N₁

Question 32

The working of dynamo is based on the principle of

Answer 32

Electromagnetic induction

Question 33

Transformation ratio in transformer is

Answer 33

V s/V p

S and p neeche

Question 34

Which of the following is correct for step-up transformer?

Answer 34

V s > V p

S and p neeche